Over the past 20 years, dynamic interactionism has been the main paradigm for the study of personality development. It is assumed that individuals develop in a dynamic, continuous, and reciprocal process of interaction, or transaction, with their environment (Caspi, 1998; Magnusson, 1988, 1990; Sameroff, 1983). In terms of social relationships, it is hypothesized that, over time, personality affects the environment and the environment affects personality (Asendorpf & Wilpers, 1998). Whereas this assumption seems justified in childhood, it is less obvious in young adulthood. Is personality already so much crystallized at the end of adolescence that it is immune to future experiences in social relationships with parents and peers? Or do important life transitions (Elder, 1985) such as the transition to the new social world of university change personality through new experiences with peers and the decreasing contact with one’s family? If students’ social relationships are destabilized during such a life transition, is the reorganization of their relationships influenced by their personality?